1. Field of the Invention
The present invention relates to a method of analyzing the magnetic field of a rotating machine.
2. Description of the Related Art
As described, for example, in a paper “Induction motor analysis by time-stepping techniques”, T. W. Preston, A. B. J. Reece and P. S. Sangha, IEEE Trans. on Magnetics, vol. 24, No. 1, pp. 471–474, 1988, a conventional rotating machine magnetic field analysis method adopts a time-stepping method of sequentially analyzing the magnetic field of a rotating machine by stepwise rotating the rotor.
In analyzing the magnetic field of a rotating machine, the rotor is stepwise rotated and a matrix equation having potentials as unknown variables is solved by a numerical solution approach such as a finite element method, generally by using an iterative solution method., Since a rotating machine is accompanied by a magnetic saturation phenomenon, a permeability changes as the function of a magnetic flux density so that iterative calculations are required which are inherent to non-linear analysis. With the above-cited rotating machine magnetic field analysis method, each time the rotor is stepwise rotated, a solution is calculated by the iterative solution method by using the solution obtained at the preceding time-step as an initial value of an unknown variable. In obtaining a solution with this method, however, it is necessary to suppress a rotation angle width narrow to some extent. This method becomes ineffective when the rotation angle width exceeds a certain value. To avoid this, the calculation is generally made by setting the initial value to 0. This requires, however, a large number of iterations necessary for obtaining a solution, taking a large calculation time.